Why is it that when someone is startled by their alarm clock and immediately stands up, they feel light-headed and can even pass out?! What exactly is the cause of this? And why doesn’t this always happen? Do certain people have a predisposition for this or not? And suppose someone has a hypovolumic condition on top of this, does this have any impact on this?
Answer
It has to do with the blood pressure in your head. If it drops, your brain gets slightly less oxygen and you become light-headed and you can even pass out. When you lie down, your body has no trouble keeping the blood pressure in your head high enough. So your blood vessels “slack” a bit. When you stand up quickly, the pressure in your head will (temporarily) drop.
If you slowly sit up, your body has time to raise the blood pressure in your head (this is done, among other things, by receptors in your carotid arteries).
In hypovolemic shock, this effect may be more pronounced.
Kind regards,
Answered by
Dr Jasper Verguts
Gynecology Obstetrics
Old Market 13 3000 Leuven
https://www.kuleuven.be/
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